ASTM E1918-21

Standard Test Method for Measuring Solar Reflectance of Horizontal and Low-Sloped Surfaces in the Field

SIGNIFICANCE AND USE
5.1 Solar reflectance is an important factor affecting the temperature of a sunlit surface and that of the near-surface ambient air temperature. The test method described herein measures the solar reflectance of surfaces in natural sunlight.
SCOPE
1.1 This test method covers the measurement of solar reflectance of various horizontal and low-sloped surfaces and materials in the field, using an albedometer or pyranometer. The test method is intended for use when the sun angle to the normal from a surface is less than 45°.  
1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 17.180.20 - Colours and measurement of light
• Technical Committee: D08 - Roofing and Waterproofing
• Drafting Committee: D08.20 - Roofing Membrane Systems

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1918 − 21
Standard Test Method for
Measuring Solar Reflectance of Horizontal and Low-Sloped
1
Surfaces in the Field
This standard is issued under the fixed designation E1918; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 inhomogeneous test site—a test site of nonuniform
solar reflectance.
1.1 This test method covers the measurement of solar
3.1.3 low-sloped surface—a surface with a tilt angle not
reflectance of various horizontal and low-sloped surfaces and
exceeding 9.5°. The roofing industry has widely accepted a
materials in the field, using an albedometer or pyranometer.
slope of less than 2:12 (16.7 %) as characteristic of a low-
The test method is intended for use when the sun angle to the
sloped roof. This corresponds to a tilt angle of approximately
normal from a surface is less than 45°.
9.5°.
1.2 This standard does not purport to address all of the
3.1.4 pyranometer—a radiometric instrument used to mea-
safety concerns, if any, associated with its use. It is the
sure the hemispherical (beam plus diffuse) solar radiant energy
responsibility of the user of this standard to establish appro-
incident upon a surface per unit time and unit surface area.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1.5 solar energy—the radiant energy originating from the
1.3 This international standard was developed in accor-
sun. Approximately 99 % of terrestrial solar energy arrives at
dance with internationally recognized principles on standard-
wavelengths between 0.3 and 2.5 μm.
ization established in the Decision on Principles for the
3.1.6 solar flux—for these measurements, the beam and
Development of International Standards, Guides and Recom-
diffuse radiance (radiative power per unit area) from the sun
mendations issued by the World Trade Organization Technical
received at ground level, expressed in watts per square meter.
Barriers to Trade (TBT) Committee.
3.1.7 solar reflectance—the fraction of solar flux reflected
by a surface.
2. Referenced Documents
2
3.1.8 test site—a location that contains one or more test
2.1 ASTM Standards:
surfaces.
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods 3.1.9 test surface—a surface whose solar reflectance is to be
E691 Practice for Conducting an Interlaboratory Study to measured with a pyranometer.
Determine the Precision of a Test Method
4. Summary of Test Method
3. Terminology
4.1 An albedometer or pyranometer is used to measure
3.1 Definitions:
incoming and reflected solar radiation for a uniform horizontal
3.1.1 albedometer—an instrument consisting of two anti-
or low-sloped surface. The solar reflectance is the ratio of the
parallel (back-to-back) pyranometers, where the upper pyra-
reflected radiation to the incoming radiation.
nometer measures incoming solar radiation and the lower
pyranometer measures solar radiation reflected from the test
5. Significance and Use
surface.
5.1 Solar reflectance is an important factor affecting the
temperature of a sunlit surface and that of the near-surface
ambient air temperature. The test method described herein
1
This test method is under the jurisdiction of ASTM Committee D08 on Roofing
measures the solar reflectance of surfaces in natural sunlight.
and Waterproofing and is the direct responsibility of Subcommittee D08.20 on
Roofing Membrane Systems.
Current edition approved Oct. 1, 2021. Published October 2021. Originally
6. Apparatus
approved in 1997. Last previous edition approved in 2016 as E1918 – 16. DOI:
10.1520/E1918-21.
6.1 Sensor—A precision spectral pyranometer (PSP) sensi-
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
tive to radiant energy in the 0.28 to 2.8 μm band is recom-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
mended. A typical pyranometer yields a linear output of
Standards volume information, refer to the standard’s Document Summary page on
–2
the ASTM website. 60.5 % between 0 and 1400 W·m and a response time of 1 s.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E1918 − 21
Specific characteristics can be obtained based on calibration by brate the instrument at the manufacturer-specified interval,
the manufacturer of the pyranometer. Other suit
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1918 − 16 E1918 − 21
Standard Test Method for
Measuring Solar Reflectance of Horizontal and Low-Sloped
1
Surfaces in the Field
This standard is issued under the fixed designation E1918; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the measurement of solar reflectance of various horizontal and low-sloped surfaces and materials in
the field, using a an albedometer or pyranometer. The test method is intended for use when the sun angle to the normal from a
surface is less than 45°.
1.2 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 albedometer—an instrument consisting of two anti-parallel (back-to-back) pyranometers, where the upper pyranometer
measures incoming solar radiation and the lower pyranometer measures solar radiation reflected from the test surface.
3.1.2 inhomogeneous test site—a test site of nonuniform solar reflectance.
3.1.3 low-sloped surfaces—surface—surfaces a surface with a slope smaller than tilt angle not exceeding 9.5°. The roofing
industry has widely accepted a slope of 2:12 or less as a definition of low-sloped roofs.less than 2:12 (16.7 %) as characteristic
of a low-sloped roof. This corresponds to a slope tilt angle of approximately 9.5° (16.7 %).9.5°.
3.1.4 pyranometer—an a radiometric instrument (radiometer) used to measure the total hemispherical (beam plus diffuse) solar
radiant energy incident upon a surface per unit time and unit surface area.
3.1.5 solar energy—the radiant energy originating from the sun. Approximately 99 % of terrestrial solar energy lies betweenarrives
at wavelengths ofbetween 0.3 to 3.5and 2.5 μm.
1
This test method is under the jurisdiction of ASTM Committee D08 on Roofing and Waterproofing and is the direct responsibility of Subcommittee D08.18 on
Nonbituminous Organic Roof Coverings.
Current edition approved Nov. 1, 2016Oct. 1, 2021. Published January 2017October 2021. Originally approved in 1997. Last previous edition approved in 20152016 as
E1918 – 06 (2015).E1918 – 16. DOI: 10.1520/E1918-16.10.1520/E1918-21.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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E1918 − 21
3.1.6 solar flux—for these measurements, the directbeam and diffuse radiation radiance (radiative power per unit area) from the
sun received at ground level over the solar spectrum, level, expressed in watts per square metre.meter.
3.1.7 solar reflectance—the fraction of solar flux reflected by a surface.
3.1.8 test site—a location that contains one or more test surfaces.
3.1.9 test surface—a surface whose solar reflectance is to be measured with a pyranometer.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 solar spectrum—the solar spectrum at ground level extending from wavelength 0.3 to 3.5 μm.
4. Summary of Test Method
4.1 A An albedometer or pyranometer is used to measure incoming and reflected solar radiation for a uniform horizontal or
low-sloped surface. The solar reflectance is the ratio of the reflected radiation to the incoming radiation.
5. Significance and Use
5.1 Solar reflectance is an important factor affecting surface and the temperature of a sunlit surface and that of the near-surface
ambient air temperature. Surfaces with low solar reflectance (typically 30 % or lower), absorb a high fraction of the incoming solar
energy which is either conducted into buildings or convected to air (leading to higher air temperatures). Use of materials with high
solar reflectance may
...